1. Field of the Invention
The present invention relates to temperature probes and more particularly to circuitry for conditioning an oven temperature probe.
2. Background Art
A search of the background art directed to the subject matter of the present invention conducted in the U.S. Patent and Trademark Office disclosed the following U.S. Letters Patent:
______________________________________ 3,699,800 3,924,101 4,546,320 4,736,091 4,761,539 4,852,544 4,906,820 4,958,062 5,029,244 ______________________________________
Additional patents known to the applicant of the present invention include the following:
______________________________________ 4,345,145 4,393,300 4,467,184 4,782,215 4,829,161 4,899,034 ______________________________________
None of the above identified patents are believed to claim, teach or disclose the novel combination of elements and function set forth in the present invention.
The intent of the present circuitry is to provide an economical means of converting a temperature variable resistance measurement of voltage over a complete range as required by most voltage converting circuits (analog to digital converters). Some of the circuits used in the past have included a capacitor charge time measurement wherein the probe is utilized as part of an RC timing network. This is particular technique, while inexpensive, highly inaccurate. Another technique incorporated pulse width modulation. While such techniques are simple, they are not very accurate and develop substantial problems at low voltages. Another approach has been to utilize a programmable resistor network to accurately vary the gain of an operational amplifier whose output is fed into a comparator. In such an arrangement, the comparator output then signals a microprocessor and a comparison between the probe voltage and that of the operational amplifier is made. Such an arrangement is quite accurate but requires a custom resistor network and several microprocessor outputs.